Rudy Giuliani’s Manhattan home has reportedly been searched by federal investigators.
The ex-New York City mayor has been under investigation for a number of years over his dealings in Ukraine.
A law enforcement official, speaking anonymously, confirmed to Associated Press that search warrants had been executed.
Sources said electronic devices were confiscated as searches took place at Mr Giuliani‘s home on Madison Avenue and his office on Park Avenue.
The probe into his business and overseas dealings stalled last year due to a dispute over tactics as Mr Giuliani, acting as President Trump’s personal lawyer, helped him dispute the US election results.
The full scope of the current investigation is unclear, a law enforcement official told AP.
Mr Giuliani was also central to Mr Trump’s attempt to press Ukraine to investigate Joe Biden and son Hunter over alleged impropriety in dealings with a Ukrainian gas firm.
The former mayor also tried to undermine America’s former ambassador to Ukraine, and met a Ukrainian politician several times who later released edited phone recordings to try to discredit Mr Biden before the election.
In a statement through his lawyer, Mr Giuliani accused authorities of a “corrupt double standard” and said the Justice Department was “running rough shod over the constitutional rights of anyone involved in, or legally defending, former President Donald J Trump”.
“Mr Giuliani respects the law, and he can demonstrate that his conduct as a lawyer and a citizen was absolutely legal and ethical,” the statement said.
Mr Giuliani helped Donald Trump’s failed bid to dispute the US election results
Federal prosecutors tried last year to obtain search warrants, including for some of Mr Giuliani’s communications, but the requests were blocked by Trump-era Justice Department officials, according to multiple AP sources.
The allegations now appear to be actively pursued once again after new attorney general Merrick Garland took office last month, with deputy Lisa Monaco sworn in last week.
Applications for search warrants served on lawyers must be signed off by senior Justice Department officials.
The US Attorney’s office in Manhattan and the FBI’s New York office declined to comment on the search warrant reports.